Spanish police and the FBI have dismantled a multimillion-dollar international art forgery ring which duped hundreds of customers into buying counterfeit prints of works purporting to be by artists including Picasso, Warhol and Dalí.Two Italians, one Spaniard and four Americans were charged in connection with two overlapping conspiracies believed to have netted about $5m (£2.5m). With the help of US gallery owners, fraudsters based in Catalonia and Italy used eBay to sell the fakes to victims in the US, Canada, Australia, Europe and Japan, US and Spanish law enforcement officials said. The bogus works were sold for between ˆ1,500 (£1,180) and ˆ20,000 to more than 1,000 clients.

Announcing the arrests at a press conference in Chicago, US attorney Patrick Fitzgerald said: "Literally thousands of people in different countries and on different continents may come to learn that when they thought they bought an original work signed by Picasso or Dalí or Chagall, they in fact bought a fake."Police were called in after complaints from American customers who realised the "masterpieces" they had been sold were cheap imitations. A joint operation was launched in 2006 between the FBI, the Mossos d'Esquadra, the Catalan regional police, and the Italian carabineri.

At a press conference in Chicago yesterday, Antoni Permanyer, head of criminal investigations for the Mossos d'Esquadra, said many gallery owners took advantage of the gullibility of buyers to sell on the fakes. Police carried out eight raids on addresses in Barcelona, one on a gallery in Granollers near Barcelona and a house in Lliçà de Munt, again near Barcelona, where officers found a thousand fakes.

The versions of works of Miró, Picasso, Dalí and Tàpies are being examined by experts and a number of professional artists in a number of museums in Spain. Tàpies, the experimental painter, is Spain's biggest selling living artist.

The Art Loss Register said the thieves' favourite artist was Picasso, followed by Miró, Chagall and then Dalí.

The European gang, which was based in Spain and Italy, shipped the counterfeit prints to art dealers in Florida and the north Chicago suburb, Northbrook. They warned dealers to shift the merchandise gradually so as not to flood the market.

At one point, the Northbrook dealer, Michael Zabrin, allegedly offered two supposed Picasso etchings, saying they were 1968 works signed by the artist in pencil and from an edition limited to 50.

A second Northbrook man, James Kennedy, was also charged with forging the signatures of Picasso, Chagall, Alexander Calder, Miró and Roy Lichtenstein, officials said. The three Europeans were named as Spaniard Oswaldo Aulestia-Bach and Italians Elio Bonfiglioli and Patrizia Soliani. In a second indictment, Zabrin and Kennedy were named in a scheme to distribute 2,500 counterfeit Calder prints and 600 Chagall prints. According to the indictment, Kennedy gained nearly $1.3m from the sale of art between 2005 and 2007.